Abstract:

A thermodynamic database for the system Fe-Cr-Ni-C-O has been built using previously assessed binary and ternary systems. Six ternary systems, Fe-Cr-O, Fe-C-O, Fe-Ni-O, Cr-Ni-O, Cr-C-O, and Ni-C-O, have been assessed. Quaternary and quinary systems were calculated using only interpolation models. This method of building a database is known as the Calphad method and it is widely used in modern thermodynamics.

An associated solution model with a non-ideally interacting species, namely 'Fe', 'Cr', 'Ni', 'C', 'FeO', 'FeO1.5', 'Cr2/3O', and 'NiO' was used for the liquid phase. The solid metallic phases were described using the sublattice model with carbon and oxygen on the second sublattice, and solid oxide phases were described using the compound energy model. The carbide phases were treated as stoichiometric or semistoichiometric phases. The optimisation was performed using the Parrot module included in the Thermo-Calc program.

The model parameters for the liquid phase in metal-oxygen systems were transformed from the parameters optimised with the ionic liquid model by other authors. Because of the new assessments of the binary systems, all the ternary systems including oxygen were optimised. Only in the Ni-C-O system could the parameters not reproduce the experimental data.

The calculated quaternary systems are in good agreement with the experimental data without using any quaternary parameters. The model parameters assessed in this work describe the system Fe-Cr-Ni-C-O well according to the experimental information from its sub systems.

The complete Gibbs energy expressions for the alloy phases were presented, allowing the calculation of the phase diagrams and thermodynamic mixing properties of the mixture phases.